Former New York Mayor Rudy Giuliani spoke at Madison Square Garden last night on the first day of the Republican National Convention. He was mayor at the time of the Sept. 11 attacks.

NEW YORK – Four years after he was an embittered and defeated candidate forced to endure the convention coronation of the man who beat him, it was a revived and reinvigorated Sen. John McCain who last night came to the aid of President Bush at the opening session of the Republican National Convention.

He was joined in that task by former New York Mayor Rudolph Giuliani, himself only eight years removed from being such a pariah inside his own party that his home-state Republicans pointedly refused to invite him to the GOP convention in San Diego.

But here, in 2004, McCain and Giuliani shared the spotlight as party mavericks who have fallen into line. With great relish, they undertook a political assignment that is crucial to Bush's re-election hopes and, as sort of a political bonus, improved both of their chances to run for higher office themselves if they choose in 2008.

The most important role belonged to McCain, the former Vietnam prisoner of war, crusader for campaign finance reform and Arizona senator who only a few months ago allowed speculation to flourish that he would jump parties to join the Democratic ticket headed by his friend, Massachusetts Sen. John Kerry.

Any ambivalence on his part about Bush, though, was missing this night. By putting aside his personal feelings toward the president and doing the bidding of his current commander in chief, McCain has emerged as a pivotal figure in the run for a second term.

Bush needs to shore up his standing with Republican moderates and to win over more skeptical independents. And no one other than Secretary of State Colin Powell has as much influence with them.

McCain showed yesterday that he is willing to flex that muscle on behalf of the man who beat him after a particularly nasty primary campaign that left the Arizona senator angry and hurt.

"He's not the type who holds a grudge," said Dan Schnur, the Californian who was McCain's press secretary in his presidential run. "The two men will probably never go on long camping trips together, but he believes that George Bush would make a better president than Kerry, so he's doing what he can to make that happen."

The passage of time has made it easier for McCain to embrace Bush and for Bush-backing Republicans to forgive McCain for his challenge. "There are four years of water under the bridge," Schnur said. "It's much easier to let bygones be bygones after four years."

It is even easier if you're Bush and you see McCain as the key to a group of voters you want badly.

"McCain represents and personifies the swing vote in America," said Republican pollster Frank Luntz. "And just as there was a Perot voter in 1992, there is a kind of McCain voter in 2004."

Luntz said the voter most likely to be swayed by McCain is "economically conservative, socially moderate and hostile to politics as we know it." It is a group that he said is currently going for Bush over Kerry by about two-to-one – a healthy margin but, according to Luntz, not healthy enough to give Bush victory.

Luntz called last night's speech "absolutely critical." He added, "This is the signal to those voters. The two most important speakers at the convention other than George W. Bush are Rudy Giuliani and John McCain."

At a time when the war in Iraq is losing public support, McCain's unyielding support for the war is especially important – and especially welcome on a day where the major story was that the president said on NBC that he now doubts that the war on terrorism can ever be won.

Luntz's assessment of the significance of McCain's speech is shared broadly across the political community, many of whom questioned the judgment of the three television networks who arbitrarily decided to make this the one night they would air nothing from Madison Square Garden.

Pollster John Zogby said it is hard to overstate the importance of McCain's backing for Bush. "He may be the most popular politician in the country, cutting across all political lines, with particularly huge numbers among Democrats," he said.

Polls show McCain is almost every Democrat's favorite Republican. But he also is strong with the Republicans Bush is weakest with – fiscal conservatives and deficit hawks. "The president has got to have 90 percent support among Republicans to win," Zogby said. "Right now, he is just a little bit short and this helps."

As proof of McCain's appeal, he has appeared in commercials for both Bush and Kerry. And he gave Kerry great cover when the Democrat's Vietnam service came under question and McCain immediately defended him.

But as impressive as McCain's political standing is, it cannot approach the change in Giuliani's standing within his party. That standing could not have been shakier for the pro-abortion rights New York mayor than it was when he endorsed Democrat Mario Cuomo for governor in 1994 and was unenthusiastic about Republican Bob Dole's 1996 candidacy for president.

"Rudy is a political deity right now," Zogby said. "He is everyone's prototype of a strong leader in a crisis."

Of course, whether that status – or the star appeal of McCain – could translate into 2008 support for president is impossible to know. McCain, even though he would be 72 then, would start the race as the favorite if only because of his huge advantage in name identification.

About the only certainty is that, after McCain's speech here, he is not about to get the endorsement of liberal filmmaker Michael Moore, who drew more boos than even Saddam Hussein.

"Whether he runs in 2008 or not, he's helped elect a president he believes is the best man for the job and he has reminded Republican primary voters that he is a good Republican," Schnur said. "Neither of those is a bad thing for him."